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[104.57.184.186]) by smtp.gmail.com with ESMTPSA id f63sm95341otb.36.2021.06.15.15.58.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Jun 2021 15:58:27 -0700 (PDT) Date: Tue, 15 Jun 2021 17:58:25 -0500 From: Bjorn Andersson To: Rob Herring Cc: Manivannan Sadhasivam , Lorenzo Pieralisi , Bjorn Helgaas , linux-arm-msm , PCI , devicetree@vger.kernel.org, "linux-kernel@vger.kernel.org" , Siddartha Mohanadoss Subject: Re: [PATCH v2 2/3] PCI: dwc: Add Qualcomm PCIe Endpoint controller driver Message-ID: References: <20210603103814.95177-1-manivannan.sadhasivam@linaro.org> <20210603103814.95177-3-manivannan.sadhasivam@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 15 Jun 17:20 CDT 2021, Rob Herring wrote: > On Tue, Jun 15, 2021 at 3:57 PM Bjorn Andersson > wrote: > > > > On Tue 15 Jun 16:40 CDT 2021, Rob Herring wrote: > > > > > On Sat, Jun 5, 2021 at 9:07 PM Bjorn Andersson > > > wrote: > > > > > > > > On Thu 03 Jun 05:38 CDT 2021, Manivannan Sadhasivam wrote: > > > > > > > > > Add driver support for Qualcomm PCIe Endpoint controller driver based on > > > > > the Designware core with added Qualcomm specific wrapper around the > > > > > core. The driver support is very basic such that it supports only > > > > > enumeration, PCIe read/write, and MSI. There is no ASPM and PM support > > > > > for now but these will be added later. > > > > > > > > > > The driver is capable of using the PERST# and WAKE# side-band GPIOs for > > > > > operation and written on top of the DWC PCI framework. > > > > > > > > > > Co-developed-by: Siddartha Mohanadoss > > > > > Signed-off-by: Siddartha Mohanadoss > > > > > [mani: restructured the driver and fixed several bugs for upstream] > > > > > Signed-off-by: Manivannan Sadhasivam > > > > > > > > Really nice to see this working! > > > > > > [...] > > > > > > > > +static void qcom_pcie_ep_configure_tcsr(struct qcom_pcie_ep *pcie_ep) > > > > > +{ > > > > > + writel_relaxed(0x0, pcie_ep->tcsr + TCSR_PCIE_PERST_EN); > > > > > > > > Please avoid _relaxed accessor unless there's a strong reason, and if so > > > > document it. > > > > > > Uhhh, what!? That's the wrong way around from what I've ever seen > > > anyone say. Have you ever looked at the resulting code on arm32 with > > > OMAP enabled? It's just a memory barrier and an indirect function call > > > on every access. > > > > > > Use readl/writel if you have an ordering requirement WRT DMA, > > > otherwise use relaxed variants. > > > > > > > That does make sense. Unfortunately I don't know where this started, but > > I would guess it might have been a reaction to the fact that people > > where just sprinkling wmb() all over the place to be on the safe side... > > I think you could write a book on it. In the beginning, there was x86 > and it was strongly ordered... > I guess it would allow me to ask people to RTFM (RTFB) instead then :) Jokes aside, I think we came to the conclusion that writel() was better than incorrect use of writel_relaxed() followed by wmb(). And in this particular case it's definitely not happening in a hot code path... > > > > > > > + writel_relaxed(0x0, pcie_ep->tcsr + TCSR_PERST_SEPARATION_ENABLE); > > > > > +} > > > > > + > > > > > > [...] > > > > > > > > +static struct platform_driver qcom_pcie_ep_driver = { > > > > > + .probe = qcom_pcie_ep_probe, > > > > > + .driver = { > > > > > + .name = "qcom-pcie-ep", > > > > > > > > Skip the indentation of the '='. > > > > > > > > > + .suppress_bind_attrs = true, > > > > > > > > Why do we suppress_bind_attrs? > > > > > > Because remove is not handled. > > > > > > > Not handled in Mani's driver, or is this a PCI thing? > > Only a PCI thing in the sense all the drivers happen to copy-n-paste > it and are mostly built-in. The Android modules thing doesn't seem to > have quite hit PCI yet. On the flipside, I'm sure there's lots of > drivers we can unbind and fun will ensue. > > There is some work needed as the remove() implementations that we do > have are all unique (such as do we need a lock or not). I keep nudging > people to look into it. > Thanks, that confirms that my expectation. I would prefer to see this tackled in a separate step then :) Regards, Bjorn